Mixing of a Viscoplastic Fluid in Cylindrical Vessels Equipped with Paddle Impellers

The mixing characteristics of a complex fluid by paddle impellers in cylindrical reactors are explored in this paper. The working fluid has a shear thinning behavior with yield stress. The Hershel-Bulkley model is used to describe the rheological behavior of fluid. The paddle impeller has two blades and it rotates at low Reynolds number varying in the range from 0.1 to 70. Effect of blade height (h/D = 0.1, 0.4, 0.7 and 0.95), blade width (d/D = 0.2, 0.4, 0.6 and 0.8) and Reynolds number on cavern size and power consumption are explored. With a great blade height, the obtained results revealed the formation of a dead zone near the blade tip at low Reynolds number. This poor mixing region disappear with a sufficient impeller rotational speed: from Re-y = 30 found with this kind of fluid. Two recirculation loops are observed with an excessive increased blade width (with d/D = 0.8 found here). The well-mixed region size will be enlarged with the rise of blade size, but with an additional energy cost. Also, the rise of Reynolds number permits a reduction in energy consumption and an enhancement in cavern size.